The fabrication of metal/polymer laminates for use in microcircuitry is a rapidly-evolving area of technology. In this field, copper is the metal of choice for providing a conductive surface for the circuit. Generally, the prior art has believed that pretreatment of the polymer and/or copper prior to forming the laminate, is necessary in order to enhance the physical bonding between the polymer and the copper at the polymer/copper interface. Typically, treated electrodeposited copper foil (commonly known as "treated ED foil") or treated wrought-copper foil is employed in laminate fabrication for microcircuitry. These forms of treated copper foil provide a surface roughness or etching into the copper foil to a depth of 0.0002 to 0.0005 inches for ED foil and 0.0001 to 0.0003 inches for wrought-copper foil. It is believed by the present inventors that the efficacy of bonding of polymer to these types of foils is based upon the formation of interstices and/or nodules on the foil surface which serve to anchor the polymer.
Attempts have been made in the past to use a separate adhesive layer or adhesion promoter in order to increase the adhesive and cohesive bonding strength thereof in the polymer/copper laminate. By way of illustration, U.K. Patent Application GB 2162124A, published on Jan. 29, 1986, discloses the use of an adhesive film of fluoropolymer/microglass to improve the bonding strength of a fluoropolymer-coated polyimide to copper foil. Although this U.K. patent application does not specify the type of copper foil used, the theory of "mechanical interlock" postulated at page 4, lines 10-12 thereof, suggests that the copper surface at the polymer/copper interface is pretreated to provide surface roughness, thus serving as a basis for mechanical interlock of the copper foil and with the polymer.
As an alternative or supplement to the use of an adhesion promoter or copper surface treatment, the prior art has utilized electrical discharge treatment of the surface of the polymer to be bonded to the copper to enhance the "cementability" of the polymer forming the laminate. For example, U.S. Pat. No. 3,676,566 discloses at column 5, lines 42-67 thereof, the use of electrical discharge in combination with a polyalkyleneimine adhesion promoter to enhance bonding in the laminate.
All of the above-described treatments of copper and/or polymer are expensive and increase laminate production time. Moreover, the use of an adhesion promoter adds to the laminate total materials cost and adds a separate and costly processing step in the fabrication of the laminates. Therefore, a new method of fabricating laminates without the need for pretreating the polymer or copper surfaces and which does not require a separate adhesion promoter would be highly desirable from a commercial standpoint.